全文获取类型
收费全文 | 3518篇 |
免费 | 56篇 |
国内免费 | 48篇 |
专业分类
航空 | 1740篇 |
航天技术 | 1206篇 |
综合类 | 31篇 |
航天 | 645篇 |
出版年
2021年 | 39篇 |
2019年 | 29篇 |
2018年 | 60篇 |
2017年 | 58篇 |
2016年 | 52篇 |
2015年 | 35篇 |
2014年 | 89篇 |
2013年 | 103篇 |
2012年 | 88篇 |
2011年 | 139篇 |
2010年 | 83篇 |
2009年 | 149篇 |
2008年 | 161篇 |
2007年 | 103篇 |
2006年 | 77篇 |
2005年 | 105篇 |
2004年 | 98篇 |
2003年 | 129篇 |
2002年 | 108篇 |
2001年 | 127篇 |
2000年 | 70篇 |
1999年 | 77篇 |
1998年 | 87篇 |
1997年 | 61篇 |
1996年 | 97篇 |
1995年 | 115篇 |
1994年 | 116篇 |
1993年 | 55篇 |
1992年 | 71篇 |
1991年 | 36篇 |
1990年 | 32篇 |
1989年 | 82篇 |
1988年 | 28篇 |
1987年 | 24篇 |
1986年 | 36篇 |
1985年 | 93篇 |
1984年 | 93篇 |
1983年 | 66篇 |
1982年 | 67篇 |
1981年 | 100篇 |
1980年 | 21篇 |
1979年 | 26篇 |
1978年 | 32篇 |
1977年 | 27篇 |
1975年 | 33篇 |
1974年 | 24篇 |
1973年 | 22篇 |
1972年 | 25篇 |
1970年 | 21篇 |
1969年 | 21篇 |
排序方式: 共有3622条查询结果,搜索用时 15 毫秒
851.
852.
Long-lived, stable jets are observed in a wide variety of systems, from protostars, through Galactic compact objects to active galactic nuclei (AGN). Magnetic fields play a central role in launching, accelerating, and collimating the jets through various media. The termination of jets in molecular clouds or the interstellar medium deposits enormous amounts of mechanical energy and momentum, and their interactions with the external medium, as well, in many cases, as the radiation processes by which they are observed, are intimately connected with the magnetic fields they carry. This review focuses on the properties and structures of magnetic fields in long-lived jets, from their launch from rotating magnetized young stars, black holes, and their accretion discs, to termination and beyond. We compare the results of theory, numerical simulations, and observations of these diverse systems and address similarities and differences between relativistic and non-relativistic jets in protostellar versus AGN systems. On the observational side, we focus primarily on jets driven by AGN because of the strong observational constraints on their magnetic field properties, and we discuss the links between the physics of these jets on all scales. 相似文献
853.
W.D. Apel J.C. Arteaga L. Bähren K. Bekk M. Bertaina P.L. Biermann J. Blümer H. Bozdog I.M. Brancus P. Buchholz S. Buitink E. Cantoni A. Chiavassa K. Daumiller V. de Souza F. Di Pierro P. Doll M. Ender R. Engel H. Falcke M. Finger D. Fuhrmann H. Gemmeke C. Grupen A. Haungs D. Heck J.R. Hörandel A. Horneffer D. Huber T. Huege P.G. Isar K.-H. Kampert D. Kang O. Krömer J. Kuijpers K. Link P. Łuczak M. Ludwig H.J. Mathes M. Melissas C. Morello S. Nehls J. Oehlschläger N. Palmieri T. Pierog J. Rautenberg H. Rebel M. Roth C. Rühle A. Saftoiu 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2011
854.
Iu.V. Cherniak I.E. Zakharenkova A. Krankowski I.I. Shagimuratov 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2012
The plasmaspheric electron content (PEC) was estimated by comparison of GPS TEC observations and FORMOSAT-3/COSMIC radio occultation measurements at the extended solar minimum of cycle 23/24. Results are retrieved for different seasons (equinoxes and solstices) of the year 2009. COSMIC-derived electron density profiles were integrated up to the height of 700 km in order to retrieve estimates of ionospheric electron content (IEC). Global maps of monthly median values of COSMIC IEC were constructed by use of spherical harmonics expansion. The comparison between two independent measurements was performed by analysis of the global distribution of electron content estimates, as well as by selection specific points corresponded to mid-latitudes of Northern America, Europe, Asia and the Southern Hemisphere. The analysis found that both kinds of observations show rather similar diurnal behavior during all seasons, certainly with GPS TEC estimates larger than corresponded COSMIC IEC values. It was shown that during daytime both GPS TEC and COSMIC IEC values were generally lower at winter than in summer solstice practically over all specific points. The estimates of PEC (h > 700 km) were obtained as a difference between GPS TEC and COSMIC IEC values. Results of comparative study revealed that for mid-latitudinal points PEC estimates varied weakly with the time of a day and reached the value of several TECU for the condition of solar minimum. Percentage contribution of PEC to GPS TEC indicated the clear dependence from the time with maximal values (more than 50–60%) during night-time and lesser values (25–45%) during day-time. 相似文献
855.
S.R. Sanderson J.M. Austin Z. Liang F. Pintgen J.E. Shepherd H.G. Hornung 《Progress in Aerospace Sciences》2010,46(2-3):116-131
We note the common existence of a supersonic jet structure locally embedded within a surrounding transonic flow field in the hitherto unrelated phenomena of unstable gaseous detonation and hypervelocity blunt body shock wave interaction. Extending prior results that demonstrate the consequences of reduced endothermic reaction rate for the supersonic jet fluid in the blunt body case, we provide an explanation for observations of locally reduced OH PLIF signal in images of the keystone reaction zone structure of weakly unstable detonations. Modeling these flow features as exothermically reacting jets with similarly reduced reaction rates, we demonstrate a mechanism for jetting of bulk pockets of unreacted fluid with potentially differing kinetic pathways into the region behind the primary detonation front of strongly unstable mixtures. We examine the impact of mono-atomic and diatomic diluents on transverse structure. The results yield insight into the mechanisms of transition and characteristic features of both weakly and strongly unstable mixtures. 相似文献
856.
Fabrizio Nicolosi Agostino De Marco Pierluigi Della Vecchia 《Aerospace Science and Technology》2013,24(1):226-240
This paper presents some results of the flight test campaign conducted on the Tecnam P2006T aircraft, on the occasion of its certification process. This twin-engine propeller airplane is certified under the normal category CS-23 and FAR 23. A prototype of this light aircraft has been tested in flight for a post-design performance optimization and for the assessment of flight qualities. These experiences have led to the application of two winglets to the original wing. The final configuration has been extensively tested for the achievement of CS-23 certification. The longitudinal and lateral-directional response modes have been assessed and quantified. At the same time the longitudinal airplane model, through a dedicated set of flight maneuvers, has been characterized by means of parameter estimation studies. The aircraft stability derivatives have been estimated from the acquired flight data using the identification technique known as Output Error Method (OEM). Some estimated stability derivatives have been also compared with the corresponding values extracted from leveled flight tests and from wind tunnel tests performed on a scaled model of the aircraft. 相似文献
857.
858.
Test requirements, which are generally collected in multiple disparate formats throughout the life cycle of an electronic product, could be used in various applications that reduce test and development cycle times and increase the confidence in the final test program. Unfortunately, test requirements are seldom captured in a consistent format that may be processed by a computer, thus eliminating the possibility of using such requirements in an engineering application. Additionally, such an approach disallows test requirements captured in one segment of the product life cycle to be reused in subsequent life cycle stages. This paper describes a model-based methodology, specifically the Test Requirements Model (TeRM), which can be shown to facilitate the transfer of test-related product information between various stages of the life cycle. This transportability, in conjunction with an exchange format that can be processed by a computer, permits test requirement information to support value-added applications in the engineering process throughout the life cycle of a product 相似文献
859.
860.